It is known to use ultrasound to image a fetus in the womb by transmission and reception of ultrasound waves from a transducer.
Three-dimensional (3D) ultrasound images may be obtained by using software to combine ultrasound data that has been taken at different positions or angles, and to render an image from the combined data using methods such as simple surface shading or direct volume rendering. In four-dimensional (4D) ultrasound imaging systems, a series of three-dimensional images obtained at different times is dynamically rendered to produce a moving 3D image, for example a 3D ultrasound movie.
In recent years, 3D and 4D ultrasound images have been made more realistic through the use of advanced lighting techniques (referred to as global illumination, gradient free lighting, subsurface scattering or photon mapping) that simulate illumination with a more physically accurate model than was previously used.
A popular objective of 3D and 4D fetal ultrasound scans (sometimes known as fetal keepsake scans) is to image the fetal face. Many parents are having 3D or 4D ultrasound scans in order to bond better with their unborn child, motivated by the realistic appearance of the scans. 3D or 4D ultrasound scans can also be useful for informing parents of the appearance of a fetus that has an abnormality such as a cleft lip or cleft palate.
Volumetric data received from ultrasound scans may be noisy. Volumetric ultrasound data may be smoothed before rendering to reduce noise in the resulting rendered image. However, the process of smoothing the volumetric image data may also reduce levels of detail in the rendered image.